The present invention relates to logic selection modules, which make it possible to select on the basis of digital data signals one out of a number of similar circuits and to transmit the desired data thereto.
Automatic telephone switchboards are known in which for the actual connection network a single standard circuit reproduced a large number of times. This circuit is known under the name symmetrical time matrix (STM) and has been described in U.S. Pat. No. 4,093,827. In order to produce spatial-time paths within the connection network, it is necessary to introduce into the STM address memories the data necessary for establishing the connections within said matrix. In its existing construction the STM comprises three input terminals, one for receiving a coupling signal which validates the two others, another for receiving a series signal giving the address of the storage position to be addressed and the final one receives a series signal giving the data to be entered in the thus designated position.
Although a single STM makes it possible to establish 256 spatial-time paths, the connection network of an automatic telephone switchboard has a large number thereof. Therefore it would not be reasonable to wish to directly connect each of the STM to the central control processor of the switchboard by three separate wires connected to the previously defined terminals. This would be even less reasonable in view of the fact that the occupation level of these terminals is relatively low, because they are only used when it is necessary to make or cut out a call. It is therefore desirable to establish a pyramid-type logic device, which, on the basis of a few output terminals of the central unit, demultiplies or divides the latter in order to be able to connect them to all the input terminals of the STM. It would obviously be possible to realize this device with known integrated circuits joined together in such a way as to give the necessary logic functions. However, it is desirable to produce such an automatic telephone switchboard with a very small number of separate circuits produced with large scale integration and whose STM is known under the trade reference EFX 7331. Other circuits have also been produced with this objective in mind and in particular the terminal switching module (TSM) making it possible to bring about the interface between the PCM junction and the input STM of the connection network. This TSM is known under the reference EFX 7333. For all these circuits it is necessary to standardize the control inputs on the basis of the three terminals defined hereinbefore with the same signals to be applied to the said terminals. Thus, the structure of the circuits for directing the control signal from the central automatic telephone switchboard unit to the standard circuits of different types and particularly the STM and TSM will be the same. To further extend standardization it would then be desirable to realize a standard circuit used in a repetitive manner and without any other circuit for producing the aforementioned interface.